Generic dual-fuel internal combustion engines are typically operated in two operating modes. We differentiate an operating mode with a primary liquid fuel supply (“liquid operation” for short; in the case of the use of diesel as a liquid fuel, it is called “diesel operation”) and an operating mode with primarily gaseous fuel supply, in which the liquid fuel serves as a pilot fuel for initiating combustion (also called “pilot operation” or “ignition jet operation”).
Whether liquid or pilot operation is selected can depend on various factors, such as the availability of fuel, economic considerations or legal requirements.
It is also known that a pilot mode can be changed to a liquid mode if the quality of the gaseous fuel decreases.
In addition, there are also mixed operations, in which the quantities of gaseous and liquid fuel are comparable.
The disadvantage to date was that it was not readily possible to safely meter even small quantities of liquid fuel, but this is necessary in pilot operation. For this purpose, either two different fuel injectors must be provided for the liquid fuel (one for larger quantities of liquid fuel and one for smaller quantities of liquid fuel), or a single fuel injector with two injector needles must be used (see e.g. WO 2014/106525 A 1).